I. Field of the Invention
This invention relates generally electrosurgical instruments, and more particularly to a bipolar electrosurgical instrument especially designed for carrying out a valvulotomy procedure on a vein to disable the venous valves.
II. Discussion of the Prior Art
Vein grafts are frequently used to replace segments of obstructed arteries for the continuation of blood flow in an arterial bypass procedure. In the case of an in situ bypass, where the vein is left essentially in place, an instrument called a valvulotome is used to render the valves in the vein inoperative. Arteries have smooth and unobstructed interior surfaces while peripheral veins have valves which insure a primary direction of blood flow back to the heart. In an in situ saphenous vein bypass, the saphenous vein, which normally returns the blood from the ankle upwardly through the leg, takes over the function of the occluded segments of femoral artery to carry blood from the leg to the ankle. In order for the segment of saphenous vein to carry on the function of the femoral artery, the series of one-way valves in the vein must be disabled.
To date, various valve stripping instruments have been devised for cutting or removing the valvular obstructions to the distal arterial flow. Instruments used for valvulotomy procedures have included single and double bullet-shape metal strippers employing incising parts of different shapes, such as described in the Ouriel et al. U.S. Pat. No. 4,952,215. Other valvulotomes have long, thin handles supporting curved, hook-like incising tips, such as is described in the Donovan U.S. Pat. No. 4,924,882. These instruments are designed to be introduced into the vein and displaced from the distal to proximal direction, and to incise the valves upon pulling the device backward so as to engage the valves cusps and cut through the valves. These mechanical valvulotomes must move forward and backward, with the cutting blades against the stationary valve cusps to cut the valves.
The use of razor sharp cutting blades inside the delicate vein poses the possibility of injury to the endothelium, as well as splitting and destruction of the vein, rendering it unsuitable as a graft. Further, the sharp mechanical devices of the prior art can accidentally engage the many side branches of the vein and cause unwanted cuts and tears. Though the precise cause for post-operative atherosclerosis is not known, endothelium injury has been discussed as a likely culprit.
When it is considered that the saphenous vein is larger toward the thigh and becomes noticeably smaller at the ankle, the current mechanical valvulotome devices are not able to accommodate the gradient in diameter of the vein. The gradation in size of the vein is addressed by repeatedly exchanging valvulotomes of different sizes at different regions of the vein. In addition to lengthening the time for the procedure, the frequent exchanging of the different sizes of valvulotomes involves additional axial movements of the device inside the vein, thus further increasing the possibility for injury to the endothelial layer. As mentioned above, in the standard procedure, using prior art valvulotomes as the different instruments are passed in moving in the proximal direction from the ankle towards the thigh, a need arises to make additional incisions along the length of the vein to allow valvulotomes of larger sizes to be inserted. This requires later suturing and creates a discontinuity in the vein which may later become the site of an atherosclerotic lesion.
In cardiac surgery, autologous reversed saphenous vein grafting has become routine for aorta-coronary bypass surgery. With this procedure, the valves within the vein are left intact, and the vein itself is reversed. The distal portion of the vein graft is usually larger in diameter than the replaced coronary artery, resulting in reduced blood flow velocity in the vein graft compared with that in the coronary artery. The patency rate of the coronary vein grafts goes from 85 percent at the end of the first year, post-operatively, to approximately 60 percent in five years. At 10 years, atherosclerosis becomes the major cause of coronary vein graft failure. Studies suggest that valves do not open fully during reverse blood flow and cause a decreased graft blood flow rate at the obstruction-related points. These intact, non-collapsed valve cusps may also cause sufficient turbulence to the laminar flow to become a situs for thrombus formation. Additional experience has shown that when more than one valve is present in the saphenous vein graft, occlusion, thrombus formation and accelerated progressive atherosclerosis seem to occur in correlation to the number of valves.
The function of a valvulotome is to disable vein valves such that a segment of vein can be used as a graft by bypass procedure without having to reverse its orientation relative to direction of blood flow.
Examples of typical prior art valvulotome devices are described in the Maloney U.S. Pat. No. 4,791,913; the Nobles U.S. Pat. No. 5,284,478; the Mehigan U.S. Pat. No. 5,171,316; the Ouriel et al. U.S. Pat. No. 4,952,215; the Quadri U.S. Pat. No. 5,133,725; and the Segalowitz U.S. Pat. No. 5,234,450.
From the foregoing discussion of the prior art, it is apparent that there is a need for an improved valvulotome which can be advanced in a retrograde direction relative to venous blood flow (proximal to distal) and operated to disable, by cutting, valve cusp material with a minimum of instrument exchanges and with minimal damage to the endothelium.